This invention relates generally to a cleaning apparatus for suspensions, in particular fibrous suspensions. More particularly, this invention relates to a cleaning apparatus in which a number of cleaners, such as hydrocyclones, are arranged in several consecutive stages, of which the initial stages comprise a plurality of cleaners arranged in parallel to form a battery, with at least one main line being provided in which a plurality of cleaners adapted to prepare three fractions are arranged in multiple stages. A first fraction is extracted from a vortex core created in the cleaner through a central extraction pipe positioned within the cleaner body, or its vortex core. This first fraction is enriched with lightweight soil to the greatest degree. A second fraction is extracted through an external extraction pipe which is arranged coaxially to the central extraction pipe. This second fraction is enriched with less lightweight soil, and partially with heavy soil. A third fraction is extracted radially outwardly from the cleaner body at its outlet aperture and is hardly enriched at all with any lightweight soil. This third fraction predominantly contains specifically heavier parts than the lightweight soil.
Cleaning apparatus for suspensions of this general type is known from the journal "Wochenblatt fur Papierfabrikation", (Weekly Magazine for Paper Manufacture), 1966, Page 389 to 400, in particular see FIGS. 8 and 11.
The precision cleaning hydrocyclones, also referred to as cleaners, used in these prior art installations are generally equipped with a thin, conical lower part in which the aperture angle of the cone is in the range of between 4.degree. and 10.degree., preferably from 6.degree.-8.degree.. These prior art cleaners are interconnected into batteries to form one stage at a time, as is known, for instance, from U.S. Pat. No. 4,462,899 and WO 84/03236.
In the apparatus known from the above-mentioned "Wochenblatt", the main quantity of accept transported in the direction of the machine reservoir, if necessary after final cleaning by means of very fine screens, has already been removed from the first stage of the main group of cleaners, which is the only group provided, and the other stages of the main group are switched in cascade.
In these cleaners of the precision cleaning stages, an attempt is made to remove the medium-weight soil completely from the fibrous suspension, to which the adhesive portions also specifically belong and which are found in particle form in the fibrous suspensions. With the prior art type of apparatus, and in particular, the prior art switching arrangements having such cleaners, the soil removal process has not been entirely satisfactory.